The present invention is in a process for removing liquid ash from a combustion gas which is produced by the combustion of coal with air under a pressure of from 2 to 30 bars, wherein the combustion gas, at a temperature between 1200.degree. and 1700.degree. C., is passed through at least one porous gas-permeable filter element which is disposed in the combustion chamber.
German Patent Application No. P 37 20 963.9 discloses a process wherein air for the combustion of the coal is introduced into the combustion chamber at such a rate that the entire carbon content of the coal is combusted to form CO.sub.2 and the resulting combustion gas still has a low carbon content. This means that in the process known from German Patent Application No. P 37 20 963.9 the combustion is carried out with a super-stoichiometric oxygen rate.
It has now been found that the useful life of the ceramic filter elements used in the known process and comprising Al.sub.2 O.sub.3, SiO.sub.2, MgO and/or ZrO.sub.2 will vary. For this reason it is an object of the invention to provide a process for the removal of liquid ash so the filter element will have a uniform useful life.